Techniques of projection television have been employed for a number of years, but hitherto the only products reaching the market on a sustained basis and in significant numbers have been expensive, large-screen units used for closed-circuit theatre presentations of sports or other special events, for background effects on news and other television broadcasts, and the like. Such units are complex, large in size, and difficult to maintain; consequently, they are not feasible for use in home entertainment, or even in places like clubs, lounges, lobbies, waiting rooms and the like, where one to a few dozen people may view them at a time.
It has previously been proposed to provide a color projection television system with a plurality of tubes each having a different color, the tubes projecting pictures superimposed in registry on a common viewing screen, as in U.S. Pat. Nos. 3,004,099 dated Oct. 10, 1961, and 2,960,615 dated Nov. 15, 1960.
Television receivers have been previously produced with the optics of a Schmidt-type projector, comprising a target illuminated in a single color by a corresponding electron beam raster, a spherical reflector, reflecting the light around the periphery of the target, and a correction lens through which the light passes to the viewing screen.
In color projection systems, substantial difficulties have attended efforts to use the Schmidt optics with each of a plurality of separate tubes in a system that can be produced for a large market, with accurate reproducibility of the tubes and correspondingly minimal adjustments by the serviceman or user in the field, whether for correction of image registration or for replacement of a tube.
The present invention has effectively overcome these difficulties by employing projection tube structures and methods adapted to achieve a high level of reproducibility of optical characteristics in production. Also, the receiver-projector is installed in a predetermined, fixed spatial relation to the screen. The combination of these characteristics assures the attainment of high-quality reception at a relatively modest cost, as compared with large-screen systems.
The features of construction and methods of production will be understood from the following description and the appended claims.